Transverse field travelling wave tube



Nov. 13, 1956 D. CHARLES TRANSVERSE FIELD TRAVELLING WAVE-TUBE 2 Sheets-Sheet 1 Filed Jan. 11, 1951 'Nov. 13, 1956 CHARLES 2,770,754

TRANSVERSE F IELD TRAVELLING WAVE TUBE Filed Jan. 11,1951 2 Sheets-Sheet 2 X/MAM, w

United States Patent TRANSVERSE FIELD TRAVELLING WAVE TUBE Daniel Charles, Paris, France, assignor to Compagnie glenerale de Telegraphie Sans Fil, a corporation of ance Application January 11, 1951, Serial No. 205,589 Claims priority, application France January 20, 1950 2 Claims. (Cl. SIS-3.5)

In copending U. S. patent application Ser. No. 150,357 of March 18, 1950, now Patent No. 2,694,783 there is described a generating device of an electronic beam in the presence of crossed electric and uniform magnetic fields. In said device, a system of two paralled plates between which exists a uniform electric field. in the presence of a uniform crossed magnetic field, furnishes an electronic beam, the characteristics of which are such that it can be transmitted into a system of two other plates parallel to each other and to the preceding ones in such a manner that the beam in the second system is displayed on the average trajectories rectilinear and parallel to the plates.

In order that the foregoing may be eifected, the beam must at its exit from the first group of plates, conform to certain conditions; in particular, it must be at a given height of the lower plate and have a velocity component directed parallel to said plate.

In the accompanying drawings: 1

Fig. 1 is a longitudinal section through a device according to said copending application;

Fig. 2 is a similar view through a device according to the invention; and

Fig. 3 is a wiring diagram showing one mode of use of the device of Fig. 2

The device of the aforementioned patent application is represented by means of Fig. 1 which shows in envelope 20 a cathodic plate 1, a source of electrons 2, 1 and 2 being a zero potential. l

3 is an anodic plate of V potential, 4 the separation plane of the beam generator and the continuation of the device described in the aforementioned patent application. 5 is the trajectory of elections issued from 2 and terminating at 4 at the distance y1 from electrode 1 with a tangent parallel to the latter, i. e. at the top of a cycloidal arch to then enter into the interaction conduit of which the delay and base electrodes are shown at 19 and 21. 6 shows the track of magnetic field H perpendicular to the plane of the figure.

Voltage V is in general fixed by the utilisation conditions of the generator. Consequently it is impossible to suitably vary the electronic intensity of the beam. Either V is great enough and the electronic source operates in saturation, the current cannot then be changed except by acting on the temperature of said source; or V is not great enough and the emission is limited by the, effect of the space charge in which case the current intensity cannot be varied.

.The present invention relates to a device allowing the regulation of the beam intensity, without the latter ceasing to have at its arrival at plane 4, the properties to be at the distance yr from electrode 21, with the tangents parallel to electrode 1.

According to the present invention, the electronic emission of a cathode in a travelling wave tube with transverse magnetic field, injecting a beam into the space between two. electrodes of an auxiliary structure parallel 2,770,754 Patented Nov. 13, 1956 t0 the delay line, is controlled by means of a grid, with adjunction of means preventing an undesirable deformation of the electronic trajectories.

It is well known that the easiest means of controlling the intensity of an electronic beam is the introduction of a grid close to the cathode, parallel to the latter.

But in the case of the tube of the present invention, owing to the existence of a magnetic field which curves the trajectories, if the introduction of a grid, positive in relation to the cathode and placed in its vicinity, allows the modulation in intensity, it also causes a deformation of trajectories in such a manner that these are subjected to a displacement parallel and perpendicular to the plates.

The present invention is based on the electric relationship that it is necessary to effect in order that the presence of a grid does not modify the conditions of the arrival of the beam at the limit 4 of the generator.

In Fig. 2, 1 is a cathodic plate, 2 an electronic source, 1 and 2 being at zero potential. 3 is an anodic plate, which is, conforming to the present invention, at potential V1, which is defined hereafter.

Plane 4 shows, as in Fig. 1, the separation between the generator and the interaction conduit, containing the forward edges of electrodes 1 and 3.

According to the present invention, 7 is a grid at potential Vg.

5 is a trajectory of electrons which, due to a suitable choice of voltage V1, arrives at plane 4 at the same distance yr from electrode 21 as before with a tangent parallel to electrode 1, the distance between plane 4 and a parallel plane passive through the center of source 2 being such that the electrons are at the top of the cycloidal arch of their trajectory.

6 is the track of magnetic field H.

The calculation shows that if d is called the distance of the two plates 1 and 3, V1 must be V is the voltage that would have to be provided if there was not a grid at potential Vg, e and m are the charge and the mass of an electron. The distance yr as seen in Fig. 2 is the algebraical sum of the distance between electrode 21 and the potential level V1 and the distance between electrode 21 and source 2.

Thus, the generator conserves all its properties, even if a positive grid is introduced, on condition that there is replaced, according to the present invention, for the voltage V of electrode 3, which would have been that of the device in the absence of the grid, a voltage V1 which depends on the voltage imposed at the grid and on voltage V.

As for a chosen generator, V is fixed as well as d and H, it is seen that Vl C-hVG Where a and b are constants, independent of the grid voltage, and V depends consequently on the mode of functioning of the generator. I

We have:

K 2eH d I ETV (5) This relation must be observed in all cases whether the grid serves to fix in a permanent manner the current intensity, or to modulate it as a function. of time.

In the latter case, the velocity variation can be very and to grid 25 of the pentode.

great, the relation (1) or its equivalent form (3) being always valid as long as the time taken by the electrons to go from 2 to 4 can be considered as small relatively to the modulation period, which is always so in practical cases.

Alp=S.AVG

If a resistance R is placed in the plate circuit and the supply voltage is called V there is on the plate, in relation to ground, a voltage It is seen that this relation is precisely the form of relation (3). It is sufiicient to suitably choose the value of R and the slope S of the tube in order that the relation (3) can be quantitatively fulfilled.

As an example, the voltage VG is therefore transmitted to the grid of a pentode, of which the slope can be chosen, by taking a variable slope tube and adjusting its polarisation. The voltage of electrode 3, that is to say V1, is taken at the exit of the pentode plate, the load resistance being suitably selected.

This assembly is shown in Fig. 3, 1 is the cathodic plate,

2 the electronic source (1 and 2 being at the same potential). 3' the anode of which the voltage V1 is defined by souce decoupled by capacitance 11, and the voltage drop in resistance 12. Grid 7 is connected to ground The screen 26 of said pentode is at fixed potential due to source 8 decoupled by capacitance 9. Plate 27 is connected to 3 and 12.

Grid 7 is maintained positive in relation to 1 due to battery decoupled by condenser 16. A counter battery 17 decoupled by condenser 18 allows the suitable polarisation of the pentode cathode in relation to its grid 25,

by fixing the slope at a desired value. 13 is a load resistance for the eventual modulation signal across capacitance 14.

The assembly of Fig. 3 is with grid connected to ground, the advantage of which is that it is not afiected by the current taken by positive grid 7 and allows the permanent functioning of the system. It should be on derstood that Fig. 3 is an example of the embodiment of the subjection of voltage V1 to grid voltage VG and consequently is non limitative for the present invention.

The system according to the present invention applicable to the high frequency amplifying tube to which the aforementioned patent application relates, is also utilisable in the cases where it must protect the cathode against an eventual bombardment by ions. The presence of a magnetic field is very effective for electrons and very slight for ions, with the result that the ions created from the source go towards anode 3 and are thus eliminated from the beam, whereas the ions coming from the beam pass above the cathode without terminating thereon.

Whatever the utilisation of the device, there is obtained a modulation of the beam intensity without a geometrical modification of the beam at its exit from the generator.

I claim:

1. An electron gun optical system, for projecting electrons in a beam into a predetermined space at a predetermined level thereof, comprising: a first and a second plane, parallel, coextensive and spaced electrodes having edges; an electron beam source positioned in the plane of said first electrode; terminal connections to said first electrode and electron beam source for applying thereto a same first potential; a terminal connection to said second electrode for applying thereto a l second potential positive with respect to said first potential, whereby an electric field is established between said first and second electrodes; means for providing, in the space bounded by said first and second electrodes, a magnetic field having its lines of force perpendicular to the direction of said electric field, wherebyth'e electrons issuing from said source'are caused to follow a cycloidal path; a grid positioned between said first and second electrodes and parallel thereto; a terminal connection to said grid for applying thereto a grid control potential; means'for controlling said second potential as a function of said grid control potential; and the distance between a first plane, passing substantially through the center of saidsource andnormal to said spaced electrodesfand a second plane, parallel to said first plane' and containing the edges of said spaced electrodes remote from said source in the direction of electron propagation, being such that the electrons issue from said space at the highest point of an arch of said, cycloidal path.

.2. A cross-field travelling wave tube, of the type including a delay line, a base electrode parallel to said delay line and defining therewith an interaction space, means for providing in said space an electric field and means for providing a magnetic field, said electric and magnetic fields being perpendicular to each other and to the direction of said delay line and base electrode, whereby there is provided within said interaction space an equipot'ential plane corresponding to the mean velocity with which electrons, when fed into said space, propagate therein under the action of said crossed fields, said tube comprising: means comprising a cathode and two electron focusing electrodes, parallel to said delay line and base electrode and defining a focusing space; means for providing in said focusing space a uniform electric field substantially less than the field in said interaction space, of same direction and parallel thereto, and for providingthe same magnetic field therein as in said interaction space; said cathode being positioned to feed electrons into said focusing space in a direction perpendicular to said focusing electrodesand parallel tothe direction of said electric field, the distance between the center of said cathode and the plane of entry of said electrons into said interaction space being substantially equal tohalf the chord of an arch of the cycloidal path imparted to'said'electrons in said focusing space under the action of said fields, the distance betweensaid equipotential plane and a parallel plane, passing through said cathode, being equal to the algebraic sum of the distance between said base electrode and the equipotential plane of same potential value in the focusing space and of the distance between said base electrode and said parallel plane, and said focusing electrodes being positioned for delivering said electrons into said interaction space as soon as they leave said focusing space; a grid parallel to said focusing electrodes and positioned therebetween; a terminal connection for applying a control potential to said grid; and means for controlling the field in said focusing space as a function of said grid control potential.

References Cited in the file of this patent UNITED STATES PATENTS 2,241,976 Blewett et al. May 13, 1941 2,371,897 Knick Mar. 20, 1945 2,372,328 Labin Mar. 27, 1945 2,414,121 Pierce Jan. 14, 1947 2,459,319 Hansell Jan. 18, 1949 2,531,972 Doehler et al. Nov. 28, 1950 2,566,087 Lerbs Aug. 28, 1951 2,607,904 Lerbs Aug. 19, 1952 OTHER REFERENCES Article by Warnecke and Doehler, pp. 279-307, Annales de Radio-electricite, October 1950, vol. 5, No. 22. 

